The flexible waveguide of this invention is based upon technology disclosed in U.S. Pat. No. 5,815,627; issued: Sep. 29, 1998; U.S. Pat. No. 5,567,471, issued: Oct. 22, 1996; and U.S. Pat. No. 5,440,664; issued: Aug. 8, 1995, which technology and teachings are meant to be incorporated herein by way of reference. The aforementioned waveguide inventions have a common inventor, James Harrington, and a common assignee, Rutgers University. In aforementioned U.S. Pat. No. 5,815,627, it was taught that waveguides are capable of guiding both IR and visible radiation. This is also a distinguishing feature of this invention. This invention, however, has fabricated a waveguide that can be tailored for use over a wide wavelength range by the use of multiple, uniform, film coatings deposited by liquid phase chemistry methods. The coatings of the inventive waveguide have an additive, are fabricated by an additive technique rather than a subtractive method, i.e. the former Ag layer as taught in the aforementioned patents, was originally depleted in part, with the establishment of the AgI layer. The AgI layer is totally absent in the present application. Even the Ag layer is only present in one embodiment thereof, and is but one selection of other metals used for the metallic underlay.
This invention utilizes dielectric layers of sulfide materials, which are built in stacked geometries to fashion unique waveguide structures.
The waveguides of the present invention can be fabricated in one of two novel ways:                (a) The dielectric layers of cadmium and lead sulfide can be applied directly to the smooth bore surface of a silica glass tube; or        (b) The dielectric layers of the cadmium and lead sulfides can be applied to a metallic surface, for example, metals selected from a group consisting of Ag, Au, Cu, Pt, Ni, Pt, Mb, and Al, which has been smoothly coated upon the smooth inner bore of the silica glass tube.        
A protective polymer coating is layered upon the outer surface of the tube in both embodiments. The dielectric layers of this invention comprise CdS and PbS, which form a unique compatibility pair, in which deposition of each material does not affect the underlying layer. These paired sulfides can be stacked in multiple, thin film layers to provide specific and unique characteristics. The sulfide layers are deposited using similar liquid-phase chemistry taught in the prior patents. The thickness of each layer can be tailored for use over a wide range of wavelengths. The measured losses for a single layer of CdS or a PbS film deposited over an Ag layer was in agreement with the prior Ag/AgI film studied at 10.6 μm for applications using CO2 IR lasers.
The CdS and PbS materials have disparate refractive indices with a ratio of about 2 to 1. This is often referred to in this technology, as the index contrast ratio. The high contrast of this layering makes possible a photonic bandgap hollow fiber. The deposit of the cadmium sulfide layer provides the transmission in the visible region.